ZTFJ0038+2030: A Long-period Eclipsing White Dwarf and a Substellar Companion

Abstract

In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with an orbital period of 10.4 hr and an undetected substellar companion. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of 0.50 ± 0.02 M ☉ and a temperature of 10,900 ± 200 K. The companion has a mass of 0.059 ± 0.004 M ☉ and is a brown dwarf. It has a radius of 0.0783 ± 0.0013 R ☉, and is one of the physically smallest transiting brown dwarfs known and likely old, ≳8 Gyr. The ZTF discovery efficiency of substellar objects transiting white dwarfs is limited by the number of epochs and as ZTF continues to collect data we expect to find more of these systems. 9 NSF Astronomy and Astrophysics Postdoctoral Fellow NSF Astronomy and Astrophysics Postdoctoral Fellow